Optical characteristic measurement device and optical characteristic measurement method suitable for spectrum measurement

ABSTRACT

A processing unit obtains a first spectrum detected in a first detection area and a first signal intensity detected in a second detection area after the light entering the housing is cut off, and then calculates a first correction spectrum by subtracting a first correction value calculated based on the first signal intensity from each component value of the first spectrum. The processing unit obtains a second spectrum detected in the first detection area and a second signal intensity detected in the second detection area while a cut-off portion is opened, and then calculates a second correction spectrum by subtracting a second correction value calculated based on the second signal intensity from each component value of the second spectrum. The processing unit calculates an output spectrum representing a measurement result by subtracting a corresponding component value of the first correction spectrum from each component value of the second correction spectrum.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical characteristic measurementdevice and an optical characteristic measurement method, andparticularly to a technique for measuring a spectrum with high accuracy.

2. Description of the Background Art

Conventionally, spectrometry has widely been used as a technique forevaluating an illuminant and the like. In an optical characteristicmeasurement device used in such spectrometry, a spectrometer (typically,a diffraction grating) is generally used to split light from anilluminant or the like, which is a measurement target, into a pluralityof wavelength components and to detect each resultant wavelengthcomponent with a photodetector. In order to minimize influence of lightother than light to be measured, the spectrometer and the photodetectorare accommodated in a housing.

Actually, however, a result of detection by the photodetector may beaffected by irregularly reflected light in the housing, light reflectedin a diffused manner at a surface of the spectrometer, light having anorder other than a measurement order, and the like. In general, suchlight is referred to as “stray light”. Various methods have beenproposed in order to suppress influence of such unintended stray light.

For example, Japanese Patent Laying-Open No. 11-030552 discloses amethod of correcting stray light by accurately estimating influence ofthe stray light generated in measurement of light guided from adispersion optical system of a spectrophotometer with a light receiverhaving a large number of light-receiving elements as a measurementconstant of the spectrophotometer and by eliminating that influence.

In addition, Japanese Patent Laying-Open No. 2002-005741 discloses aspectrum measurement device capable of obtaining an accurate spectrumintensity signal by eliminating influence of stray light generatedwithin the spectrum measurement device or unnecessary light generated byreflection or diffraction at a surface of a detection element throughprocessing of a detection signal.

According to the stray light correction method disclosed in JapanesePatent Laying-Open No. 11-030552, however, it is necessary to calculatea ratio between intensity of a light reception signal measured by eachlight-receiving element and intensity of a light reception signalmeasured by the light-receiving element corresponding to the splitwavelength, as many times as the number of light-receiving elementsconstituting a detector. Therefore, this method is relativelytime-consuming.

In addition, specific details of correction processing are not disclosedwith regard to the spectrum measurement device described in JapanesePatent Laying-Open No. 2002-005741.

SUMMARY OF THE INVENTION

The present invention was made to solve such a problem, and an object ofthe present invention is to provide an optical characteristicmeasurement device and an optical characteristic measurement methodcapable of measuring a spectrum in a shorter period of time with highaccuracy.

An optical characteristic measurement device according to one aspect ofthe present invention includes a housing, a spectrometer arranged in thehousing, a cut-off portion for cutting off light entering thespectrometer from outside of the housing, a photodetector arranged inthe housing, for receiving light split by the spectrometer, and aprocessing unit for outputting a result of detection by thephotodetector. The photodetector has a detection surface greater than alight incident surface receiving light from the spectrometer. Theprocessing unit is operative to obtain a first spectrum detected in afirst detection area corresponding to the light incident surfacereceiving light from the spectrometer and a first signal intensitydetected in a second detection area different from the light incidentsurface receiving light from the spectrometer while the light enteringthe housing is cut off, calculate a first correction spectrum bysubtracting a first correction value calculated based on the firstsignal intensity from each component value of the first spectrum, obtaina second spectrum detected in the first detection area and a secondsignal intensity detected in the second detection area while the cut-offportion is opened, calculate a second correction spectrum by subtractinga second correction value calculated based on the second signalintensity from each component value of the second spectrum, andcalculate an output spectrum representing a measurement result bysubtracting each component value of the first correction spectrum from acorresponding component value of the second correction spectrum.

Preferably, the optical characteristic measurement device furtherincludes a cut-off filter arranged on an optical path through whichlight taken into the housing enters the spectrometer, for cutting offlight having a wavelength shorter than a prescribed wavelength.

More preferably, the second detection area is provided on a shortwavelength side continuing from the first detection area.

Preferably, the second detection area includes a plurality of detectionelements. The first correction value is an average value of first signalintensities detected by the plurality of detection elementsrespectively, and the second correction value is an average value ofsecond signal intensities detected by the plurality of detectionelements respectively.

Preferably, the processing unit includes a storage unit for storing thefirst correction spectrum.

An optical characteristic measurement device according to another aspectof the present invention includes a housing, a spectrometer arranged inthe housing, a photodetector arranged in the housing, for receivinglight split by the spectrometer, and a processing unit for outputting aresult of detection by the photodetector. The photodetector has adetection surface greater than a light incident surface receiving lightfrom the spectrometer. The processing unit is operative to obtain ameasurement spectrum detected in a first detection area corresponding tothe light incident surface receiving light from the spectrometer and asignal intensity detected in a second detection area different from thelight incident surface receiving light from the spectrometer, calculatea first correction spectrum by correcting a pattern prepared in advanceand exhibiting a noise characteristic of the photodetector based on thesignal intensity, calculate a second correction spectrum by subtractinga correction value calculated based on the signal intensity from eachcomponent value of the measurement spectrum, and calculate an outputspectrum representing a measurement result by subtracting each componentvalue of the first correction spectrum from a corresponding componentvalue of the second correction spectrum.

Preferably, the processing unit stores a plurality of patterns incorrespondence with a plurality of exposure times that can be set in thephotodetector and selects one pattern corresponding to the exposure timeset in the photodetector when the first correction spectrum is to becalculated.

An optical characteristic measurement method according to yet anotheraspect of the present invention includes the step of preparing ameasurement device including a spectrometer and a photodetector forreceiving light split by the spectrometer, that are arranged in ahousing. The photodetector has a detection surface greater than a lightincident surface receiving light from the spectrometer. The opticalcharacteristic measurement method includes the steps of obtaining afirst spectrum detected in a first detection area corresponding to thelight incident surface receiving light from the spectrometer and a firstsignal intensity detected in a second detection area different from thelight incident surface receiving light from the spectrometer while lightentering the housing is cut off, calculating a first correction spectrumby subtracting a first correction value calculated based on the firstsignal intensity from each component value of the first spectrum,obtaining a second spectrum detected in the first detection area and asecond signal intensity detected in the second detection area while acut-off portion is opened, calculating a second correction spectrum bysubtracting a second correction value calculated based on the secondsignal intensity from each component value of the second spectrum, andcalculating an output spectrum representing a measurement result bysubtracting each component value of the first correction spectrum from acorresponding component value of the second correction spectrum.

An optical characteristic measurement method according to yet anotheraspect of the present invention includes the step of preparing ameasurement device including a spectrometer and a photodetector forreceiving light split by the spectrometer, that are arranged in ahousing. The photodetector has a detection surface greater than a lightincident surface receiving light from the spectrometer. The opticalcharacteristic measurement method includes the steps of obtaining ameasurement spectrum detected in a first detection area corresponding tothe light incident surface receiving light from the spectrometer and asignal intensity detected in a second detection area different from thelight incident surface receiving light from the spectrometer,calculating a first correction spectrum by correcting a pattern preparedin advance and exhibiting a noise characteristic of the photodetectorbased on the signal intensity, calculating a second correction spectrumby subtracting a correction value calculated based on the signalintensity from each component value of the measurement spectrum, andcalculating an output spectrum representing a measurement result bysubtracting each component value of the first correction spectrum from acorresponding component value of the second correction spectrum.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing appearance of an optical characteristicmeasurement device according to an embodiment of the present invention.

FIG. 2 is a functional block diagram showing overview of the measurementdevice according to the embodiment of the present invention.

FIG. 3 is a schematic diagram showing a detection surface of aphotodetector according to the embodiment of the present embodiment.

FIG. 4 is a conceptual diagram showing an exemplary detection resultoutput from the photodetector in the optical characteristic measurementdevice according to the embodiment of the present invention.

FIG. 5 is a schematic configuration diagram showing a hardwareconfiguration of a processing device according to the embodiment of thepresent invention.

FIG. 6 is a flowchart showing a measurement procedure in an opticalcharacteristic measurement device according to the related art of thepresent invention.

FIG. 7 is a flowchart showing a processing procedure for darkmeasurement in the optical characteristic measurement device accordingto the embodiment of the present invention.

FIG. 8 is a flowchart showing a processing procedure for ordinarymeasurement in the optical characteristic measurement device accordingto the embodiment of the present invention.

FIG. 9 is a schematic diagram showing a control structure in theprocessing device of the optical characteristic measurement deviceaccording to the embodiment of the present invention.

FIG. 10 is a diagram showing an exemplary stray light evaluation resultas to the optical characteristic measurement device according to theembodiment of the present invention.

FIGS. 11A to 11C are enlarged views of a substantial part of a spectrumshown in FIG. 10.

FIG. 12 is a functional block diagram showing overview of a measurementinstrument main body according to a first variation of the embodiment ofthe present invention.

FIG. 13 is a diagram showing temperature dependency of a darkmeasurement result according to the embodiment of the present invention.

FIGS. 14A to 14C show measurement results showing temperature dependencyof a dark spectrum according to the embodiment of the present invention.

FIGS. 15A to 15C are diagrams showing dark patterns obtained from darkspectra shown in FIGS. 14A to 14C.

FIG. 16 is a diagram showing a measurement result indicating exposuretime dependency of the dark measurement result according to theembodiment of the present invention.

FIGS. 17A to 17C are diagrams showing other measurement resultsindicating exposure time dependency of the dark measurement resultaccording to the embodiment of the present invention.

FIG. 18 is a diagram showing a measurement example using an opticalcharacteristic measurement device according to the first variation ofthe embodiment of the present invention.

FIG. 19 is a schematic diagram showing a control structure in aprocessing device of the optical characteristic measurement deviceaccording to the first variation of the embodiment of the presentinvention.

FIG. 20 is a flowchart showing a measurement procedure in the opticalcharacteristic measurement device according to the first variation ofthe embodiment of the present invention.

FIG. 21 is a schematic diagram showing a substantial part of a controlstructure in a processing device of an optical characteristicmeasurement device according to a second variation of the embodiment ofthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described in detail withreference to the drawings. The same or corresponding elements in thedrawings have the same reference characters allotted, and descriptionthereof will not be repeated.

<Overall Configuration of Device>

Referring to FIG. 1, an optical characteristic measurement device 1according to the embodiment of the present invention measures a spectrumof various illuminants (hereinafter also referred to as an “object”). Inaddition, optical characteristic measurement device 1 may calculate suchoptical characteristics as brightness and tint of the object based onthe measurement spectrum. It is noted that brightness refers toluminance, luminous intensity and the like of the object, and tintrefers to a chromaticity coordinate, a dominant wavelength, excitationpurity, a correlated color temperature, and the like of the object.Optical characteristic measurement device 1 according to the presentembodiment is applicable to measurement for a light emitting diode(LED), a flat panel display (FPD), and the like.

Optical characteristic measurement device 1 includes a measurementinstrument main body 2 and a processing device 100. A light receptionportion 6 is connected to measurement instrument main body 2 through anoptical fiber 4. Light emitted from the object and taken in from lightreception portion 6 (hereinafter also referred to as “measured light”)is guided to measurement instrument main body 2 through optical fiber 4.

As will be described later, measurement instrument main body 2 splitsthe measured light that enters measurement instrument main body 2 fromthe object and outputs a result of detection in accordance withintensity of each wavelength component included therein (signalintensity) to processing device 100. As will be described later,measurement instrument main body 2 contains a spectrometer for splittingmeasured light and a photodetector for receiving light split by thespectrometer. In particular, the photodetector according to the presentembodiment has a detection surface greater than a light incident rangereceiving light from the spectrometer. In addition, processing device100 outputs the result of detection by the photodetector as it iscorrected. More specifically, processing device 100 simultaneouslyobtains a spectrum detected in a detection area corresponding to a lightincident surface receiving light from the spectrometer in the detectionsurface of the photodetector and a signal intensity detected in adetection area different from the light incident surface receiving lightfrom the spectrometer, independently of each other. Then, processingdevice 100 eliminates an error component originating from stray lightand an offset component caused by a dark current that flows in thephotodetector by subtracting a correction value calculated based on theobtained signal intensity from each component value of the spectrum. Byperforming such processing, the spectrum of the measured light from theobject can be measured in a shorter period of time with high accuracy.

<Configuration of Measurement Instrument Main Body>

FIG. 2 is a functional block diagram showing overview of measurementinstrument main body 2 according to the embodiment of the presentinvention. Referring to FIG. 2, measurement instrument main body 2includes a shutter 21, a slit 22, a cut-off filter 23, a spectrometer24, and a photodetector 25. These components are accommodated in ahousing 26. A light input port 20 is formed in a part of housing 26.Light input port 20 is connected to optical fiber 4. The measured lightguided by optical fiber 4 enters housing 26 and propagates along aprescribed optical axis Ax. Shutter 21, slit 22, cut-off filter 23, andspectrometer 24 are arranged along this optical axis Ax, sequentiallyfrom light input port 20. Namely, the measured light enters spectrometer24 after it passes through slit 22 and cut-off filter 23.

Shutter 21 cuts off light that enters housing 26 from the outside ofhousing 26. Namely, shutter 21 establishes such a state that light doesnot enter housing 26, in order to obtain a spectrum serving as acalibration reference of the result of detection by photodetector 25(hereinafter also referred to as a “dark spectrum”). For example,shutter 21 is structured such that it can be displaced in a directionperpendicular to optical axis Ax. Thus, when shutter 21 is located onoptical axis Ax (hereinafter also referred to as a “close position”),light that enters housing 26 is cut off. It is noted that an operationfor measuring a dark spectrum detected by photodetector 25 while thelight that enters housing 26 is cut off is also referred to as “darkmeasurement”. On the other hand, for distinction from this “darkmeasurement”, an ordinary operation for measuring a spectrum of anobject is also referred to as “ordinary measurement”.

When shutter 21 is located at a position distant from optical axis Ax(hereinafter also referred to as an “open position”), the measured lightenters housing 26. Though FIG. 2 illustrates arrangement where shutter21 is provided inside housing 26, it may be provided outside housing 26.In addition, a mechanism of any type may be employed as a mechanism forcutting off measured light.

Slit 22 adjusts a diameter of luminous flux (size) of the measured lightin order to attain prescribed detection resolution. For example, eachslit width of slit 22 is set approximately to 0.2 mm to 0.05 mm. Themeasured light after passing through slit 22 enters cut-off filter 23.It is noted that cut-off filter 23 is arranged at a positionsubstantially corresponding to a focus position of the measured lightafter passing through slit 22.

Cut-off filter 23 is arranged on optical axis Ax, which is an opticalpath through which the measured light taken into housing 26 entersspectrometer 24. Cut-off filter 23 cuts off light having a wavelengthshorter than a prescribed cut-off wavelength a among components includedin this measured light. Namely, cut-off filter 23 allows transmissiononly of light having a wavelength longer than prescribed cut-offwavelength α. As will be described later, this cut-off wavelength apreferably matches with a lower limit value of a spectral characteristicof spectrometer 24 (wavelength f_(min)).

Spectrometer 24 is arranged on optical axis Ax and splits the measuredlight incident along optical axis Ax into a plurality of wavelengths.The light having wavelengths resulting from spectrometer 24 is guided tophotodetector 25. For example, spectrometer 24 is implemented by aconcave diffraction grating (grating) called blazed holographic type.This concave diffraction grating reflects incident measured light towardcorresponding directions as diffraction light having prescribedwavelength intervals. Therefore, the light split by spectrometer 24(diffraction light) is emitted toward photodetector 25 in a spatiallyspread manner.

Instead of the blazed holographic type concave diffraction gratingdescribed above, any diffraction grating such as a flat focus typeconcave diffraction grating may be adopted as spectrometer 24.

Photodetector 25 receives the measured light (diffraction light) splitby spectrometer 24. Photodetector 25 detects an intensity of eachwavelength component included in the received measured light. Theintensity detected by photodetector 25 is brought in correspondence witheach wavelength component. Accordingly, the detection signal fromphotodetector 25 corresponds to the spectrum of the measured light.Photodetector 25 is representatively implemented by a photodiode array(PDA), in which a plurality of detection elements such as photodiodesare arranged in an array. Alternatively, a charge coupled device (CCD)in which a plurality of detection elements such as photodiodes arearranged in matrix may be adopted. For example, photodetector 25 isconfigured to be able to output signals indicating intensities of 512wavelength components (channels) in a range from 380 nm to 980 nm. Inaddition, photodetector 25 includes an A/D (Analog to Digital) converterfor outputting a signal indicating a detected light intensity as adigital signal and a peripheral circuit.

<Overview of Correction Processing>

Correction processing in optical characteristic measurement device 1according to the present embodiment will be described hereinafter withreference to FIGS. 1, 3 and 4. The result of detection by photodetector25 includes (1) a spectrum to be measured of the measured light, (2) anerror component originating from stray light generated within housing26, (3) an offset component caused by a dark current that flows inphotodetector 25, and (4) other error components.

Stray light is collective denotation of irregularly reflected light inhousing 26, light reflected in a diffused manner at the surface ofspectrometer 24, and light having an order other than a measurementorder generated in spectrometer 24.

In addition, photodetector 25 is implemented by a semiconductor devicesuch as a CCD, and a dark current flows when such a semiconductor deviceis driven. Due to this dark current, the result of detection byphotodetector 25 may contain an offset component. In addition, magnitudeof the dark current is susceptible to an ambient temperature and it mayfluctuate over time, depending on an environment for measurement.

Accordingly, in optical characteristic measurement device 1 according tothe present embodiment, in the detection surface of photodetector 25, anarea where diffraction light from spectrometer 24 enters and an areawhere the diffraction light does not enter are provided. Then,processing device 100 corrects the result detected in the area wherediffraction light enters with the result detected in the area wherediffraction light does not enter. Namely, by making such correction eachtime ordinary measurement is conducted, influence of stray light and theoffset component caused by the dark current can dynamically becorrected. Therefore, even when influence of stray light and/or theoffset component caused by the dark current fluctuate(s) over time,correction can effectively be made.

FIG. 3 is a schematic diagram showing the detection surface ofphotodetector 25 according to the embodiment of the present embodiment.Referring to FIG. 3, it is assumed that spectrometer 24 (FIG. 2) isoptically designed such that a wavelength component in a range from awavelength f_(min) to a wavelength f_(max) of the incident measuredlight is guided to photodetector 25.

Here, it is assumed that cut-off wavelength a of cut-off filter 23 isset to match with wavelength f_(min). Here, a wavelength componentshorter than wavelength f_(min) (cut-off wavelength α) does not enterspectrometer 24. Therefore, a wavelength component shorter thanwavelength f_(min) (cut-off wavelength α) does not enter photodetector25 either.

In the detection surface of photodetector 25, an area corresponding tothe range from wavelength f_(min) to wavelength f_(max) (hereinafteralso referred to as a “measurement wavelength range”) is defined as adetection area 25 a. Namely, detection area 25 a is an areacorresponding to the light incident surface receiving light fromspectrometer 24. In addition, a prescribed range on a short wavelengthside continuing from detection area 25 a (hereinafter also referred toas a “correction wavelength range”) is defined as a correction area 25b. Though the entire range on the side of a wavelength shorter thanwavelength f_(min) may be handled as correction area 25 b, in order toavoid influence of the measured light, detection area 25 a andcorrection area 25 b are preferably distant from each other by aprescribed wavelength width.

Referring again to FIG. 2, stray light generated in housing 26 can beregarded as uniformly diffusing. Therefore, stray light incident on thedetection surface of photodetector 25 can be regarded as substantiallyequal. Namely, the intensity of stray light incident on each of theplurality of detection elements constituting detection area 25 a andcorrection area 25 b is substantially identical to each other.

In addition, detection area 25 a and correction area 25 b are providedon common photodetector 25. Accordingly, the offset component caused bythe dark current that is included in the detection result in detectionarea 25 a and correction area 25 b can also be regarded as substantiallyuniform.

Based on the consideration as above, photodetector 25 outputs thedetection result as shown in FIG. 4.

FIG. 4 is a conceptual diagram showing an exemplary detection resultoutput from photodetector 25 in optical characteristic measurementdevice 1 according to the embodiment of the present invention.

Referring to FIG. 4, the detection result output from photodetector 25includes an error component 40 originating from stray light. Errorcomponent 40 can be regarded as having a uniform signal intensity over adetectable wavelength range. In addition, the detection result includesan offset component 50 caused by the dark current that flows in theplurality of detection elements included in photodetector 25. Offsetcomponent 50 depends on an ambient temperature and it also fluctuatesover time.

In addition, in the measurement wavelength range, a signal intensity inaccordance with the spectrum of the measured light appears. On the otherhand, in the correction wavelength range, a signal intensity inaccordance with the measured light does not appear.

Therefore, the error component originating from stray light and theoffset component caused by the dark current can be eliminated bysubtracting the correction value calculated based on the signalintensity detected in correction area 25 b (FIG. 3) from each componentvalue of a measurement spectrum detected in detection area 25 a (FIG.3). Consequently, a true spectrum of the measured light can be obtained.It is noted that correction area 25 b is preferably set to include aplurality of detection elements, and in this case, a plurality of signalintensities can be detected. Therefore, a value representative of signalintensities detected by respective detection elements included incorrection area 25 b (typically, an average value or an intermediatevalue) is preferably employed as the correction value.

In addition, in the optical characteristic measurement device accordingto the present embodiment, the dark spectrum detected by photodetector25 while light does not enter housing 26 is also corrected so as toeliminate the error component originating from stray light and theoffset caused by the dark current as described above, and the resultantdark spectrum is stored as a reference value. The corrected darkspectrum stored as the reference value does not include (1) ameasurement value of the measured light, (2) the error componentoriginating from stray light generated in housing 26, and (3) the offsetcomponent caused by the dark current that flows in photodetector 25.Namely, the corrected dark spectrum reflects an error factor specific toeach device, such as variation among detection elements.

Therefore, in each measurement, the spectrum of the measured light canbe measured with high accuracy, by subtracting the signal intensitydetected in correction area 25 b (FIG. 3) and the corrected darkspectrum from the measurement spectrum detected by photodetector 25. Inaddition, in every ordinary measurement, as it is not necessary to openand close shutter 21 (FIG. 2) only for measuring the error componentoriginating from stray light and/or the offset component caused by thedark current, the time required for measurement can be shortened.

<Configuration of Processing Device>

Referring again to FIG. 1, processing device 100 is representativelyimplemented by a computer. More specifically, processing device 100includes a computer main body 101 incorporating an FD (Flexible Disk)drive 111 and a CD-ROM (Compact Disk-Read Only Memory) drive 113, amonitor 102, a keyboard 103, and a mouse 104. As computer main body 101executes a program stored in advance, the correction processingdescribed above is provided.

FIG. 5 is a schematic configuration diagram showing a hardwareconfiguration of processing device 100 according to the embodiment ofthe present invention. Referring to FIG. 5, computer main body 101includes, in addition to FD drive 111 and CD-ROM drive 113 shown in FIG.1, a CPU (Central Processing Unit) 105, a memory 106, a fixed disk 107,and a communication interface (I/F) unit 109, that are connected to eachother through a bus.

An FD 112 is attachable to FD drive 111, and a CD-ROM 114 is attachableto CD-ROM drive 113. Processing device 100 according to the presentembodiment is implemented by execution of a program by CPU 105 usingcomputer hardware such as memory 106. In general, such a program isdistributed as it is stored in a non-transitory storage medium such asFD 112 or CD-ROM 114 or through a network or the like. Such a program isthen read from a storage medium by means of FD drive 111, CD-ROM drive113, or the like and once stored in fixed disk 107 representing astorage device. In addition, the program is read from fixed disk 107 tomemory 106 and executed by CPU 105.

CPU 105 serves as an operation processing unit for performing variousoperations by sequentially executing programmed instructions. Memory 106temporarily stores various types of information as CPU 105 executes theprogram.

Communication interface unit 109 is a device for mediating datacommunication between computer main body 101 and measurement instrumentmain body 2 (FIG. 1). Communication interface unit 109 receives anelectric signal indicating measurement data transmitted from measurementinstrument main body 2 and converts the signal into a data formatadapted to processing by CPU 105, and converts an instruction or thelike output by CPU 105 into an electric signal and sends the signal tomeasurement instrument main body 2.

Monitor 102 connected to computer main body 101 is a display device fordisplaying a calculation result such as brightness or tint of the objectthat is calculated by CPU 105, and it is implemented, for example, by aliquid crystal display (LCD) or a cathode ray tube (CRT).

Keyboard 103 accepts an instruction from a user through an input key.Mouse 104 accepts an instruction from a user through an operation suchas clicking or sliding.

In addition, other output devices such as a printer may be connected tocomputer main body 101 as necessary.

<Measurement Procedure>

For facilitating understanding of the correction processing in opticalcharacteristic measurement device 1 according to the present embodiment,a measurement procedure in connection with the related art of thepresent invention will initially be described.

(1. Processing Procedure in Connection with Related Art)

FIG. 6 is a flowchart showing the measurement procedure in an opticalcharacteristic measurement device according to the related art of thepresent invention. It is noted that FIG. 6 shows a processing procedurewhere dark measurement is conduced each time ordinary measurement isconducted.

Referring to FIG. 6, the processing device determines whether ameasurement start instruction has been provided or not (step S300). Whenthe measurement start instruction has not been provided (NO in stepS300), the processing device waits until the measurement startinstruction is provided. Before the measurement start instruction isprovided, positioning of the object and/or the light reception portionis carried out such that light emitted from the object is taken into thelight reception portion.

On the other hand, when the measurement start instruction is provided(YES in step S300), initially, dark measurement shown in step S302 andstep S304 is conducted. Specifically, the processing device drives theshutter to the close position (step S302). Namely, a state that light isprevented from entering the housing is established. In succession, theprocessing device obtains the spectrum detected by the photodetector asthe dark spectrum (step S304).

In succession, ordinary measurement shown in steps S306 to S310 isconducted. Specifically, the processing device drives the shutter to theopen position (step S306). Namely, the measured light is taken into thehousing. In succession, the processing device obtains the spectrumdetected by the photodetector as the measurement spectrum (step S308).In addition, the processing device calculates an output spectrum bysubtracting the corresponding component value of the dark spectrumobtained in step S304 from each component value of the measurementspectrum obtained in step S308 (step S310). The output spectrum isoutput as the detection result.

Thereafter, whether a measurement stop instruction has been provided ornot is determined (step S312). When the measurement stop instruction hasnot been provided (NO in step S312), the process returns to step S300.

On the other hand, when the measurement stop instruction is provided(YES in step S312), the process ends.

(2. Processing Procedure According to the Present Embodiment)

In optical characteristic measurement device 1 according to the presentembodiment, prior to a series of ordinary measurement procedures, darkmeasurement is conducted. After the dark measurement is conducted,ordinary measurement of the object is conducted. The processingprocedure will be described hereinafter with reference to FIGS. 7 and 8.

FIG. 7 is a flowchart showing the processing procedure for darkmeasurement in optical characteristic measurement device 1 according tothe embodiment of the present invention. FIG. 8 is a flowchart showingthe processing procedure for ordinary measurement in opticalcharacteristic measurement device 1 according to the embodiment of thepresent invention.

Referring to FIG. 7, processing device 100 determines whether a darkmeasurement start instruction has been provided or not (step S100). Whenthe dark measurement start instruction has not been provided (NO in stepS100), processing device 100 waits until the dark measurement startinstruction is provided.

On the other hand, when the dark measurement start instruction isprovided (YES in step S100), processing device 100 drives shutter 21 tothe close position (step S102). Namely, a state that light is preventedfrom entering housing 26 is established. In succession, processingdevice 100 obtains the spectrum detected in detection area 25 a ofphotodetector 25 (dark spectrum) and the signal intensity detected incorrection area 25 b of photodetector 25 (step S104). In succession,processing device 100 calculates the correction value based on thesignal intensity detected in correction area 25 b (step S106). Morespecifically, processing device 100 calculates an average value of aplurality of signal intensities detected in correction area 25 b as thecorrection value.

In addition, processing device 100 calculates the correction darkspectrum by (uniformly) subtracting the correction value calculated instep S106 from each component value (signal intensity) included in thedark spectrum detected in detection area 25 a, that was obtained in stepS104 (step S108). Namely, processing device 100 calculates thecorrection dark spectrum by correcting the dark spectrum with thecorrection value calculated based on the signal intensity detected incorrection area 25 b. In addition, processing device 100 has thecorrection dark spectrum calculated in step S108 stored (step S110).

Thereafter, processing device 100 drives shutter 21 to the open position(step S112). Thus, optical characteristic measurement device 1 enters ameasurement state. Then, the dark measurement ends.

Referring next to FIG. 8, processing device 100 determines whether themeasurement start instruction has been provided or not (step S200). Whenthe measurement start instruction has not been provided (NO in stepS200), processing device 100 waits until the measurement startinstruction is provided. Before the measurement start instruction isprovided, positioning of the object and/or light reception portion 6 iscarried out such that light emitted from the object is taken into lightreception portion 6.

On the other hand, when the measurement start instruction is provided(YES in step S200), processing device 100 obtains the measurementspectrum detected in detection area 25 a of photodetector 25 and thesignal intensity detected in correction area 25 b of photodetector 25(step S202). As shutter 21 is driven to the open position after thepreviously conducted dark measurement, optical characteristicmeasurement device 1 has entered a measurement state that shutter 21corresponding to the cut-off portion is open.

In succession, processing device 100 calculates the correction valuebased on the signal intensity detected in correction area 25 b (stepS204). More specifically, an average value of a plurality of signalintensities detected in correction area 25 b is calculated as thecorrection value.

In addition, processing device 100 calculates a correction measurementspectrum by (uniformly) subtracting the correction value calculated instep S204 from each component value (signal intensity) included in themeasurement spectrum detected in detection area 25 a, that was obtainedin step S202 (step S206). Namely, processing device 100 calculates thecorrection measurement spectrum by correcting the measurement spectrumwith the correction value calculated based on the signal intensitydetected in correction area 25 b. Moreover, processing device 100calculates an output spectrum by subtracting the corresponding componentvalue of the correction dark spectrum calculated in previously conducteddark spectrum (step S108) from each component value of the correctionmeasurement spectrum calculated in step S206 (step S208). This outputspectrum is output as the detection result.

Thereafter, whether the measurement stop instruction has been providedor not is determined (step S210). When the measurement stop instructionhas not been provided (NO in step S210), the process returns to stepS200.

On the other hand, when the measurement stop instruction is provided(YES in step S210), the process ends.

As described above, in optical characteristic measurement device 1according to the present embodiment, it is not necessary to conduct darkmeasurement each time ordinary measurement is conducted. Therefore, thetime required for ordinary measurement can be shortened.

<Control Structure>

FIG. 9 is a schematic diagram showing a control structure in processingdevice 100 of optical characteristic measurement device 1 according tothe embodiment of the present invention.

Referring to FIG. 9, processing device 100 according to the presentembodiment includes buffers 202, 212, 220, and 240, a correction valuecalculation unit 204, selectors 214, 218, 222, 226, and 232, subtractionunits 216 and 224, and a memory 230. FIG. 9 exemplarily shows a controlstructure corresponding to an example where detection area 25 a (FIG. 3)corresponding to the measurement wavelength range has N detectionelements and correction area 25 b corresponding to the correctionwavelength range has four detection elements.

A value detected in detection area 25 a of photodetector 25 (signalintensity at each wavelength) is temporarily stored in buffer 212. Inaddition, a value detected in correction area 25 b of photodetector 25(signal intensity) is temporarily stored in buffer 202. Buffer 212 hasat least N partitioned areas (1 ch, 2 ch, . . . , Nch) corresponding innumber to the detection elements included in detection area 25 a.Moreover, buffer 202 has at least four partitioned areas (Ach, Bch, Cch,Dch) corresponding in number to the detection elements included incorrection area 25 b. It is noted that data stored in buffers 202 and212 is sequentially updated every detection cycle (for example, severalmsec to several ten msec) of photodetector 25. Further, a channel (ch)is brought in correspondence with a wavelength detected by photodetector25.

Correction value calculation unit 204 calculates a correction value ΔMbased on the signal intensity detected in correction area 25 b andstored in buffer 202. Specifically, correction value calculation unit204 calculates an average value (or an intermediate value) of foursignal intensities stored in buffer 202 as correction value ΔM.

Selector 214 and subtraction unit 216 subtract correction value ΔM fromeach component value of the dark spectrum or the measurement spectrumdetected in detection area 25 a. More specifically, selector 214sequentially reads the signal intensity at each wavelength (channel)stored in buffer 212 in response to a clock signal CLOCK and outputs thesignal intensity to subtraction unit 216. Subtraction unit 216 subtractscorrection value ΔM from the signal intensity input from selector 214and outputs the result to selector 218. Therefore, subtraction unit 216outputs the result of subtraction of correction value ΔM from the signalintensity at each wavelength stored in buffer 212.

Selector 218 determines whether the obtained spectrum is either the darkspectrum or the measurement spectrum, in accordance with a state ofoptical characteristic measurement device 1 (dark measurement orordinary measurement), a state of opening and closing of shutter 21, andthe like. Then, selector 218 causes any one of buffer 220 and memory 230to sequentially store a result value output from subtraction unit 216,in response to clock signal CLOCK common to selector 214.

Buffer 220 temporarily stores the correction measurement spectrum andmemory 230 stores the correction dark spectrum in a non-volatile manner.Preferably, the correction dark spectrum is stored in a non-volatilemanner until another dark measurement is conducted after darkmeasurement is completed, because the correction dark spectrum isrepeatedly used in ordinary measurement.

Namely, during dark measurement, buffer 212 stores the signal intensityat each wavelength indicating the dark spectrum. Here, selector 218causes memory 230 to sequentially store the result obtained by uniformlysubtracting correction value ΔM by means of subtraction unit 216. On theother hand, during ordinary measurement, buffer 212 stores the signalintensity at each wavelength indicating the measurement spectrum. Here,selector 218 causes buffer 220 to sequentially store the result obtainedby uniformly subtracting correction value ΔM by means of subtractionunit 216. Namely, assuming that the signal intensity at each wavelengthof the spectrum stored in buffer 212 is denoted as A(i) {where 1≦i≦n}, acorrected spectrum B(i) stored in buffer 220 or memory 230 can beexpressed as shown below.B(i)=A(i)−ΔM {where 1≦i≦n}

In addition, selector 214 and selector 218 are in synchronization witheach other, in response to clock signal CLOCK. Therefore, for example,the signal intensity read from 1 ch of buffer 212 is stored in 1 ch ofbuffer 220 or 1 ch of memory 230.

Selectors 222, 226 and 232 and subtraction unit 224 calculate the outputspectrum by subtracting the corresponding component value of thecorrection dark spectrum from each component value of the correctionmeasurement spectrum. More specifically, in response to clock signalCLOCK, selector 222 sequentially reads the signal intensity at eachwavelength (channel) of the correction measurement spectrum stored inbuffer 220 and outputs the signal intensity to subtraction unit 224.Similarly, in response to clock signal CLOCK common to selector 222,selector 232 sequentially reads the signal intensity at each wavelength(channel) of the correction dark spectrum stored in memory 230 andoutputs the signal intensity to subtraction unit 224. Subtraction unit224 subtracts the signal intensity input from selector 232 from thesignal intensity input from selector 222 and outputs the result toselector 226. In addition, selector 222 and selector 232 operate insynchronization with each other in response to clock signal CLOCK.

Selector 226 causes buffer 240 to sequentially store the result valueoutput from subtraction unit 224 in response to clock signal CLOCKcommon to selectors 222 and 232.

Therefore, buffer 240 stores the result of subtraction of thecorresponding component value of the correction dark spectrum from eachcomponent value of the correction measurement spectrum. Namely, assumingthat the signal intensity at each wavelength of the correctionmeasurement spectrum stored in buffer 220 is denoted as S(i) {where1≦i≦N} and the signal intensity at each wavelength of the correctiondark spectrum stored in memory 230 is denoted as D(i) {where 1≦i≦N}, anoutput spectrum M(i) stored in buffer 240 can be expressed as shownbelow.M(i)=S(i)−D(i) {where 1≦i≦N}

This output spectrum stored in buffer 240 is output as the measurementresult.

The control structure shown in FIG. 9 is provided typically bydevelopment and execution by CPU 105 (FIG. 5) of a program stored infixed disk 107 (FIG. 5) or the like on memory 106 (FIG. 5). It is notedthat the control structure shown in FIG. 9 may partially or entirely beprovided by hardware.

In addition, though FIG. 9 illustrates a configuration adopting serialoperation processing with regard to the signal intensity at eachwavelength, such parallel operation processing as subtraction of spectrasimultaneously in respective channels may be adopted. Alternatively, anyoperation method may be adopted so long as arithmetic operationprocessing as described above can be implemented.

<Measurement Example>

An exemplary actual measurement result regarding an effect of reducingerrors originating from stray light or the like in opticalcharacteristic measurement device 1 according to the present embodimentdescribed above will be shown below.

As a method for evaluating influence of stray light, conditions forperformance of a spectrophotometer as to “stray light” are defined inJapanese Industrial Standards JIS Z8724:1997 “Methods of colormeasurement—light source color.” Under this JIS, performance ineliminating errors caused by stray light in the correction processingaccording to the present embodiment was evaluated. In addition, forcomparison, a measurement result obtained when the correction processingaccording to the present embodiment was not applied is also shown. Evenwhen the correction processing is not applied, the correction processingfor eliminating the offset component caused by the dark current from thedetection value of photodetector 25 was performed, as in the measurementprocedure shown in FIG. 6 above.

JIS above defines evaluation of stray light by using a tungsten lamp asa light source of the measured light. Specifically, initially, an outputfrom the photodetector with regard to light emitted from the tungstenlamp (a reference value) is obtained. Then, outputs from thephotodetector when sharp cut-off filters having transmission thresholdwavelengths of 500±5 (nm), 560±5 (nm) and 660±5 (nm) respectively areinserted in an incident optical path of the light emitted from thetungsten lamp are obtained. It is noted that the outputs to be evaluatedare those values at 450 (nm), 500 (nm) and 600 (nm), respectively.Finally, a ratio of each output to the reference value is calculated asa value for evaluating stray light (a stray light ratio).

In the present measurement example, three sharp cut-off filters havingtransmission threshold wavelengths of 495 (nm), 550 (nm) and 665 (nm)respectively were used for evaluation.

FIG. 10 is a diagram showing an exemplary stray light evaluation resultas to optical characteristic measurement device 1 according to theembodiment of the present invention. FIGS. 11A to 11C show partiallyenlarged views of a spectrum shown in FIG. 10.

FIG. 10 shows measurement examples in a state where no cut-off filter isinserted (reference) and in a state where each sharp cut-off filter isinserted. As shown in FIG. 10, it can be seen that a wavelength shorterthan the corresponding transmission threshold wavelength is cut off as aresult of insertion of the sharp cut-off filter.

FIG. 11A shows difference in signal intensity in the vicinity of 450(nm) depending on whether the correction processing is performed or not,in an example where the sharp cut-off filter having the transmissionthreshold wavelength of 495 (nm) is inserted. In addition, FIG. 11Bshows difference in signal intensity in the vicinity of 550 (nm)depending on whether the correction processing is performed or not, inan example where the sharp cut-off filter having the transmissionthreshold wavelength of 550 (nm) is inserted. Moreover, FIG. 11C showsdifference in signal intensity in the vicinity of 600 (nm) depending onwhether the correction processing is performed or not, in an examplewhere the sharp cut-off filter having the transmission thresholdwavelength of 665 (nm) is inserted.

In the examples shown in any figures, it can be seen that the output isclose to a zero value by applying the correction processing according tothe present embodiment.

The results as above are summarized in the table shown below. It isnoted that the “reduction ratio” in the table indicates a ratio inmagnitude of the stray light ratio in an example where the correctionprocessing is applied to the stray light ratio in an example where thecorrection processing is not applied.

Correction Processing Correction Processing Evaluation ReferencePerformed Not Performed Wavelength Signal Signal Stray Light SignalStray Light Reduction (nm) Intensity Intensity Ratio (%) Intensity Ratio(%) Ratio (%) 450 0.09 0.0001 0.11 0.0003 0.37 29.7 500 0.19 0.0002 0.100.0004 0.22 45.5 600 0.50 0.0003 0.05 0.0005 0.10 50.0

As shown in the table above, it can be seen that the stray light ratiocan be reduced to half or lower by applying the correction processingaccording to the present embodiment.

<Function and Effect in the Present Embodiment>

According to the embodiment of the present invention, on the detectionsurface of photodetector 25, the area where light split by spectrometer24 is incident (detection area 25 a) and the area where light split byspectrometer 24 is not incident (correction area 25 b) are provided.During measurement, a spectrum and an intensity value are simultaneouslyobtained from each of detection area 25 a and correction area 25 b.Then, the correction value is calculated based on the intensity valuedetected in correction area 25 b. In addition, the corrected spectrum iscalculated by subtracting the calculated correction value from eachcomponent value (signal intensity at each wavelength) of the spectrumdetected in detection area 25 a.

The correction value as described above is a value reflecting an errorcomponent originating from stray light generated in the housing and anoffset component caused by a dark current that flows in photodetector25. Therefore, by correcting the spectrum detected in detection area 25a with such a correction value, a true spectrum of the measured lightcan accurately be obtained.

In addition, according to the embodiment of the present invention, aspectrum and an intensity value are simultaneously obtained from each ofdetection area 25 a and correction area 25 b provided on identicalphotodetector 25. Therefore, even when the error component originatingfrom stray light generated in the housing and/or the offset componentcaused by the dark current that flows in photodetector 25fluctuate/fluctuates over time, such an error component can reliably beeliminated. Namely, an error due to disturbance caused by anenvironmental factor such as an ambient temperature can more reliably beeliminated.

Moreover, it is not necessary to conduct dark measurement in order toobtain the error component originating from stray light generated in thehousing and/or the offset component caused by the dark current thatflows in photodetector 25. Therefore, as it is not necessary to open andclose the shutter each time measurement is conducted, the time requiredfor measurement can be shortened.

Further, according to the embodiment of the present invention, furthercorrection is carried out by using the dark spectrum subjected tocorrection as described above (correction dark spectrum). Therefore, thespectrum output as the measurement result is free from an errorcomponent other than the error component originating from stray lightand the offset component caused by the dark current. The spectrum of theobject can thus more accurately be measured.

[First Variation]

In the embodiment described above, a configuration in which darkmeasurement is conducted prior to ordinary measurement so as to obtainthe dark spectrum and the correction dark spectrum in advance has beenillustrated. In the present variation, a configuration not requiringdark measurement will be illustrated.

<Overall Configuration of Device>

FIG. 12 is a functional block diagram showing overview of a measurementinstrument main body 2# according to a first variation of the embodimentof the present invention. Measurement instrument main body 2# shown inFIG. 12 corresponds to measurement instrument main body 2 shown in FIG.2 with shutter 21 being excluded. As measurement instrument main body 2#is otherwise the same as measurement instrument main body 2, detaileddescription will not be repeated.

<Dark Spectrum Characteristics>

Initially, a result of actual measurement of dark spectrumcharacteristics by using photodetector 25 will be illustrated.

(1. Temperature Dependency)

FIG. 13 is a diagram showing temperature dependency of a darkmeasurement result according to the embodiment of the present invention.Measurement results shown in FIG. 13 show change over time of outputsobtained when the measurement instrument main body was arranged in anisothermal layer and a temperature in the isothermal layer was varied.More specifically, the temperature in the isothermal layer was initiallyset to 10° C., and after 30 minutes have elapsed since start ofmeasurement, the temperature in the isothermal layer was varied to 20°C. In addition, FIG. 13 shows measurement results of both of the darkspectrum (the correction processing not performed) and the correctiondark spectrum (the correction processing performed). It is noted that anexposure time of photodetector 25 was set to 20 sec. A spectrum width ofthe dark spectrum and the correction dark spectrum was set to 250 to 750nm, and an average value of output values at every 50 nm within thisspectrum width was adopted as the measurement result.

As shown in FIG. 13, it can be seen that the output value of the darkspectrum (the correction processing not performed) fluctuates, beingaffected by variation in an ambient temperature. In contrast, it can beseen that the correction dark spectrum (the correction processingperformed) is hardly affected by variation in the ambient temperature.

FIGS. 14A to 14C show measurement results showing temperature dependencyof the dark spectrum according to the embodiment of the presentinvention. FIGS. 15A to 15C are diagrams showing dark patterns obtainedfrom the dark spectra shown in FIGS. 14A to 14C.

FIG. 14A shows the dark spectrum when the ambient temperature was set to10° C., FIG. 14B shows the dark spectrum when the ambient temperaturewas set to 20° C., and FIG. 14C shows the dark spectrum when the ambienttemperature was set to 30° C. It is noted that the exposure time inphotodetector 25 was also set to 20 sec as in FIG. 13.

Comparing the dark spectra shown in FIGS. 14A to 14C with one another,it can be seen that they are different in the absolute value of theamplitude corresponding to the same wavelength. Namely, it can be seenthat the characteristic of the dark spectrum is affected by the ambienttemperature.

FIGS. 15A to 15C show results of division of each component value of thedark spectrum (signal intensity at each wavelength) shown in FIGS. 14Ato 14C by the component value (signal intensity) at the shortestwavelength of the corresponding dark spectrum. Namely, FIGS. 15A to 15Cshow wavelength characteristics obtained by normalizing the dark spectrain FIGS. 14A to 14C (which are referred to as a “dark pattern” fordistinction from the dark spectrum indicating an actual amplitude).

Comparing the dark patterns shown in FIGS. 15A to 15C with one another,it can be seen that the dark patterns have substantially the samevariation characteristic.

According to the measurement results shown above, it can be concludedthat the characteristic of the dark spectrum output from photodetector25 varies depending on the ambient temperature, whereas the dark patternexhibits substantially the same characteristic regardless of the ambienttemperature.

(2. Exposure Time Dependency)

FIG. 16 is a diagram showing a measurement result indicating exposuretime dependency of the dark measurement result according to theembodiment of the present invention. FIGS. 17A to 17C are diagramsshowing other measurement results indicating exposure time dependency ofthe dark measurement result according to the embodiment of the presentinvention.

Measurement results shown in FIG. 16 show dark spectra obtained when theexposure time was set to 200 msec and 2000 msec while the ambienttemperature of photodetector 25 was maintained constant.

As shown in FIG. 16, it can be seen that, as the exposure time islonger, an amount of light energy that enters photodetector 25 increasesand hence the amplitude of the measured dark spectrum has also becomegreat.

FIG. 17A shows the dark spectrum when the exposure time in photodetector25 was set to 2000 msec, FIG. 17B shows the dark spectrum when theexposure time in photodetector 25 was set to 200 msec, and FIG. 17Cshows the dark spectrum when the exposure time in photodetector 25 wasset to 20 msec. In any example, the ambient temperature of photodetector25 was set constant.

Comparing the dark spectra shown in FIGS. 17A to 17C with one another,it can be seen that magnitude of the amplitude fluctuates depending onthe exposure time. As shown in FIGS. 17B and 17C, when the exposure timeis relatively short, the absolute value itself of the detected signalintensity has become small, and hence the spectrum characteristic doesnot clearly appear.

According to the measurement results shown above, it can be concludedthat the characteristic of the dark spectrum output from photodetector25 varies depending on the exposure time. It is noted that the darkspectrum is mainly dependent on the dark current included in the outputfrom photodetector 25. The dark current in photodetector 25 is dependenton a period during which photodetector 25 is active, that is, on anamount of accumulated charges. Therefore, in principle, it can beconcluded that the amplitude of the dark spectrum is in proportion to alogarithmic value of the exposure time in photodetector 25.

<Overview of Correction Processing>

An optical characteristic measurement device 1A according to the presentvariation calculates an output spectrum by subtracting a correspondingcomponent value of a correction dark spectrum from each component valueof a correction measurement spectrum, as in optical characteristicmeasurement device 1 according to the embodiment described above.

FIG. 18 is a diagram showing a measurement example using opticalcharacteristic measurement device 1A according to the first variation ofthe embodiment of the present invention. FIG. 18 shows a measurementexample as to measured light having the shortest wavelength atapproximately 380 nm. Namely, in a wavelength range shorter than theshortest wavelength of the measured light, the measurement result afterstray light correction (a correction measurement spectrum signal′)should attain to zero. Actually, however, due to various factors asdescribed above, the measurement result does not attain to zero.Therefore, by correcting correction measurement spectrum signal′ with acorrection dark spectrum dark′, a result further reflecting a truemeasurement value (signal′−dark′) can be obtained.

The optical characteristic measurement device shown in the presentvariation dynamically determines the correction dark spectrum necessaryfor the calculation processing as described above without conductingdark measurement. Thus, ordinary measurement can be started sooner.

More specifically, a correction dark pattern exhibiting a noisecharacteristic of photodetector 25 is prepared in advance, and thecorrection dark spectrum is determined (estimated) by multiplying thiscorrection dark pattern by the amplitude measured in ordinarymeasurement. The correction dark pattern thus determined reflects theambient temperature during ordinary measurement. As described above, asthe amplitude (signal intensity) of the correction dark spectrumfluctuates depending on the exposure time, the present variation adoptsa configuration where a plurality of correction dark patterns areprepared in correspondence with a plurality of exposure times that canbe set in photodetector 25. Namely, in each ordinary measurement, onecorrection dark pattern corresponding to the exposure time set inphotodetector 25 is selected and the correction dark spectrum isdetermined based on the selected correction dark pattern.

As will be described later, a common correction dark pattern may beprepared and the correction dark spectrum may be determined so as toreflect the ambient temperature and the exposure time in ordinarymeasurement.

<Control Structure>

FIG. 19 is a schematic diagram showing a control structure in aprocessing device 100A of the optical characteristic measurement deviceaccording to the first variation of the embodiment of the presentinvention.

Referring to FIG. 19, processing device 100A according to the presentvariation additionally includes a correction dark pattern storage unit260, selectors 262 and 268, and a multiplication unit 264, as comparedwith processing device 100 shown in FIG. 9. These components dynamicallydetermine the correction dark spectrum described above.

More specifically, correction dark pattern storage unit 260 stores aplurality of correction dark patterns 261 for respective exposure timesthat can be set in photodetector 25. Each correction dark pattern 261 isdefined by at least N partitioned component values (1 ch, 2 ch, . . . ,Nch) corresponding in number to the detection elements included indetection area 25 a.

Selector 262 and multiplication unit 264 dynamically determine thecorrection dark spectrum in cooperation. More specifically, selector 262selects correction dark pattern 261 corresponding to the exposure timeset in photodetector 25, from among the plurality of correction darkpatterns 261 stored in correction dark pattern storage unit 260.Selector 262 sequentially reads the component value (ratio) of selectedcorrection dark pattern 261 and outputs it to multiplication unit 264,in response to clock signal CLOCK.

Multiplication unit 264 calculates the correction dark spectrum bymultiplying the component value (ratio) input from selector 262 bycorrection value ΔM. Namely, in the present variation, correction valueΔM is used as a parameter reflecting the ambient temperature. This isbecause correction value ΔM reflects a value of stray light independentof the measured light, and assuming that magnitude of this stray lightis substantially constant, a factor in fluctuation of the amplitude ofcorrection value ΔM can be regarded as influence of the ambienttemperature. Therefore, the correction dark spectrum of interest can bedetermined (estimated) by multiplying correction dark pattern 261corresponding to the exposure time set in photodetector 25 by correctionvalue ΔM.

In the present embodiment, the plurality of correction dark patterns 261are experimentally obtained in advance as values normalized withcorrection value ΔM. It is considered that each of these correction darkpatterns 261 often has a value specific to photodetector 25. Therefore,the plurality of correction dark patterns 261 may be determined, forexample, by actually conducting measurement at the time of inspectionbefore shipment or the like of measurement instrument main body 2according to the present variation.

Namely, assuming that the component value at each wavelength ofcorrection dark pattern 261 stored in correction dark pattern storageunit 260 is denoted as P(i) {where 1≦i≦N}, a signal intensity D(i){where 1≦i≦N} at each wavelength of the correction dark spectrum storedin memory 230 can be expressed as follows.D(i)=ΔM×P(i) {where 1≦i≦N}

Selector 268 causes memory 230 to sequentially store each componentvalue of the correction dark spectrum output from multiplication unit264, in response to clock signal CLOCK common to selector 262.

As described above, since the operation performed after each componentvalue of the correction dark spectrum is stored in memory 230 is thesame as in processing device 100 shown in FIG. 9 above, detaileddescription will not be repeated.

<Measurement Procedure>

As described above, as optical characteristic measurement device 1Aaccording to the present variation calculates the correction darkspectrum by using the correction dark pattern prepared in advance, darkmeasurement as described above is not necessary. A measurement procedureaccording to the present variation will be described hereinafter withreference to FIG. 20.

FIG. 20 is a flowchart showing the measurement procedure in opticalcharacteristic measurement device 1A according to the first variation ofthe embodiment of the present invention.

Referring to FIG. 20, processing device 100A determines whether themeasurement start instruction has been provided or not (step S400). Whenthe measurement start instruction has not been provided (NO in stepS400), processing device 100A waits until the measurement startinstruction is provided. Before the measurement start instruction isprovided, positioning of the object and/or light reception portion 6 iscarried out such that light emitted from the object is taken into lightreception portion 6.

On the other hand, when the measurement start instruction is provided(YES in step S400), processing device 100A obtains the measurementspectrum detected in detection area 25 a of photodetector 25 and thesignal intensity detected in correction area 25 b of photodetector 25(step S402). In addition, processing device 100A calculates thecorrection value based on the signal intensity detected in correctionarea 25 b (step S404). More specifically, an average value of aplurality of signal intensities detected in correction area 25 b iscalculated as the correction value.

In succession, processing device 100A calculates the correctionmeasurement spectrum by (uniformly) subtracting the correction valuecalculated in step S404 from each component value (signal intensity)included in the measurement spectrum detected in detection area 25 a,that was obtained in step S402 (step S406). Namely, processing device100A calculates the correction measurement spectrum by correcting themeasurement spectrum with the correction value calculated based on thesignal intensity detected in correction area 25 b.

In parallel to the above, processing device 100A reads the correctiondark pattern corresponding to the set exposure time among the pluralityof correction dark patterns prepared in advance (step S408). Insuccession, processing device 100A determines the correction darkspectrum by multiplying each component value of the read correction darkpattern by correction value ΔM (step S410).

In succession, processing device 100A calculates the output spectrum bysubtracting the corresponding component value of the correction darkspectrum calculated in step S410 from each component value of thecorrection measurement spectrum calculated in step S406 (step S412).This output spectrum is output as the detection result.

Thereafter, processing device 100A determines whether the measurementstop instruction has been provided or not (step S414). When themeasurement stop instruction has not been provided (NO in step S414),the process returns to step S400.

On the other hand, when the measurement stop instruction is provided(YES in step S414), the process ends.

As described above, in optical characteristic measurement device 1Aaccording to the present variation, it is not necessary to conduct darkmeasurement in advance. Therefore, the time required for ordinarymeasurement can further be shortened.

<Function and Effect in the Present Embodiment>

According to optical characteristic measurement device 1A in the presentvariation, the correction dark spectrum that can be obtained in darkmeasurement is dynamically determined based on the correction darkpattern prepared in advance. Therefore, it is not necessary to conductdark measurement prior to ordinary measurement. Consequently, it is notnecessary to provide a shutter for cutting off disturbance light thatenters the measurement instrument main body. Accordingly, the structureof the measurement instrument main body can further be simplified andmanufacturing cost can also be reduced.

[Second Variation]

In the first variation of the embodiment of the present inventiondescribed above, a configuration in which a plurality of correction darkpatterns are prepared in correspondence with a plurality of exposuretimes that can be set in photodetector 25 has been illustrated, however,a common correction dark pattern may be prepared and the correction darkspectrum may be determined such that the ambient temperature and theexposure time are reflected. A configuration for determining thecorrection dark spectrum based on such a common correction dark patternwill be illustrated hereinafter.

As the structure of the measurement instrument main body according tothe present variation is the same as that of the measurement instrumentmain body according to the first variation shown in FIG. 12, detaileddescription will not be repeated.

As a control structure in a processing device according to the presentvariation is different from the control structure in the processingdevice according to the first variation shown in FIG. 19 only in aconfiguration for determining the correction dark spectrum, thisdifferent configuration will be described hereinafter.

FIG. 21 is a schematic diagram showing a substantial part of the controlstructure in the processing device of the optical characteristicmeasurement device according to a second variation of the embodiment ofthe present invention.

Referring to FIG. 21, the processing device according to the presentvariation includes a common correction dark pattern storage unit 270, aselector 272, a logarithmic operation unit 274, a multiplication unit276, selector 268, and memory 230.

Common correction dark pattern storage unit 270 stores a commoncorrection dark pattern. This common correction dark pattern is definedby at least N partitioned component values (1 ch, 2 ch, . . . , Nch)corresponding in number to the detection elements included in detectionarea 25 a.

Selector 272, logarithmic operation unit 274 and multiplication unit 276dynamically determine the correction dark spectrum in cooperation. Asthe amplitude of the correction dark spectrum is in proportion to alogarithmic value of the exposure time in photodetector 25, logarithmicoperation unit 274 and multiplication unit 276 correct the commoncorrection dark pattern with the logarithmic value of the exposure time.At the same time, multiplication unit 276 corrects the common correctiondark pattern with correction value ΔM. Thus, the correction darkspectrum reflecting the exposure time and the ambient temperature at thetime of measurement can be determined based on the common correctiondark pattern.

More specifically, selector 272 sequentially reads each component valueof the common correction dark pattern stored in common correction darkpattern storage unit 270 and outputs it to multiplication unit 276.Receiving the exposure time in photodetector 25, logarithmic operationunit 274 outputs the logarithmic value thereof. Multiplication unit 276calculates the correction dark spectrum by multiplying the componentvalue (ratio) input from selector 272 by the logarithmic value of theexposure time which is the correction value and correction value ΔM. Thecorrection dark spectrum is stored in memory 230 through selector 268.

Since the operation performed after each component value of thecorrection dark spectrum is stored in memory 230 is the same as inprocessing device 100 shown in FIG. 9 above, detailed description willnot be repeated.

As described above, since it is only necessary to prepare a commoncorrection dark pattern in advance in the optical characteristicmeasurement device according to the present variation, the configurationcan be more simplified, as compared with an example where a plurality ofcorrection dark patterns are prepared.

[Third Variation]

In the first and second variations of the embodiment of the presentinvention described above, a configuration in which the correction darkpattern obtained by normalizing the correction dark spectrum is obtainedin advance has been illustrated, however, a dark pattern obtained bynormalizing the dark spectrum may be obtained in advance. Namely, any ofthe correction dark pattern and the dark pattern may be adopted as thepattern exhibiting the noise characteristic of photodetector 25.

Here, for example, in the control structure (FIG. 19) in processingdevice 100A according to the first variation described above, a darkpattern storage unit for storing a plurality of dark patterns obtainedfor respective exposure times is provided instead of correction darkpattern storage unit 260. Then, selector 262 and multiplication unit 264dynamically determine the dark spectrum.

Here, as not the correction dark spectrum but the dark spectrum isdetermined, processing for correcting the dark spectrum to thecorrection dark spectrum is further performed. Typically, a subtractionunit similar to subtraction unit 216 is provided in a stage subsequentto multiplication unit 264 shown in FIG. 19, and this subtraction unitsubtracts correction value ΔM from each component value of the darkspectrum output from multiplication unit 264. The correction darkspectrum is thus obtained. As the subsequent processing is the same asin the first variation described above, detailed description will not berepeated.

Similarly, in the control structure (FIG. 21) in the processing deviceaccording to the second variation described above, a common dark patternstorage unit for storing a common dark pattern is provided instead ofcommon correction dark pattern storage unit 270. Then, selector 272,logarithmic operation unit 274 and multiplication unit 276 dynamicallydetermine the dark spectrum. In addition, processing for correcting thedetermined dark spectrum to the correction dark spectrum is furtherperformed. Typically, a subtraction unit similar to subtraction unit 216(FIG. 19) is provided in a stage subsequent to multiplication unit 276shown in FIG. 21, and this subtraction unit subtracts correction valueΔM from each component value of the dark spectrum output frommultiplication unit 276. The correction dark spectrum is thus obtained.As the subsequent processing is the same as in the second variationdescribed above, detailed description will not be repeated.

[Fourth Variation]

In the embodiment described above, an example where measurementinstrument main body 2 and processing device 100 are implemented asindependent devices respectively has been illustrated, however, thesedevices may be integrated.

[Fifth Variation]

The program according to the present invention may invoke a necessarymodule from among program modules provided as a part of an operationsystem (OS) of the computer at prescribed timing in prescribed sequencesand to cause the module to perform processing. Here, the program itselfdoes not include the module above but processing is performed incooperation with the OS. Such a program not including a module may alsobe encompassed in the program according to the present invention.

In addition, the program according to the present invention may beprovided in a manner incorporated in a part of another program. In thatcase as well, the program itself does not include a module included inanother program above but processing is performed in cooperation withanother program. Such a program incorporated in another program may alsobe encompassed in the program according to the present invention.

Moreover, the functions implemented by the program according to thepresent invention may partially or entirely be implemented by dedicatedhardware.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the scopeof the present invention being interpreted by the terms of the appendedclaims.

1. An optical characteristic measurement device, comprising: a housing;a spectrometer arranged in said housing; a cut-off portion for cuttingoff light entering said spectrometer from outside of said housing; aphotodetector arranged in said housing, for receiving light split bysaid spectrometer; and a processing unit for outputting a result ofdetection by said photodetector, said photodetector having a detectionsurface greater than a light incident surface receiving light from saidspectrometer, and said processing unit being operative to obtain a firstspectrum detected in a first detection area corresponding to said lightincident surface receiving light from said spectrometer and a firstsignal intensity detected in a second detection area different from saidlight incident surface receiving light from said spectrometer while saidlight entering said housing is cut off, calculate a first correctionspectrum by subtracting a first correction value calculated based onsaid first signal intensity from each component value of said firstspectrum, obtain a second spectrum detected in said first detection areaand a second signal intensity detected in said second detection areawhile said cut-off portion is opened, calculate a second correctionspectrum by subtracting a second correction value calculated based onsaid second signal intensity from each component value of said secondspectrum, and calculate an output spectrum representing a measurementresult by subtracting each component value of said first correctionspectrum from a corresponding component value of said second correctionspectrum.
 2. The optical characteristic measurement device according toclaim 1, further comprising a cut-off filter arranged on an optical paththrough which light taken into said housing enters said spectrometer,for cutting off light having a wavelength shorter than a prescribedwavelength.
 3. The optical characteristic measurement device accordingto claim 2, wherein said second detection area is provided on a shortwavelength side continuing from said first detection area.
 4. Theoptical characteristic measurement device according to claim 1, whereinsaid second detection area includes a plurality of detection elements,said first correction value is an average value of first signalintensities detected by said plurality of detection elementsrespectively, and said second correction value is an average value ofsecond signal intensities detected by said plurality of detectionelements respectively.
 5. The optical characteristic measurement deviceaccording to claim 1, wherein said processing unit includes a storageunit for storing said first correction spectrum.
 6. An opticalcharacteristic measurement method, comprising the steps of: preparing ameasurement device including a spectrometer and a photodetector forreceiving light split by said spectrometer, that are arranged in ahousing, said photodetector having a detection surface greater than alight incident surface receiving light from said spectrometer; obtaininga first spectrum detected in a first detection area corresponding tosaid light incident surface receiving light from said spectrometer and afirst signal intensity detected in a second detection area differentfrom said light incident surface receiving light from said spectrometerwhile light entering said housing is cut off; calculating a firstcorrection spectrum by subtracting a first correction value calculatedbased on said first signal intensity from each component value of saidfirst spectrum; obtaining a second spectrum detected in said firstdetection area and a second signal intensity detected in said seconddetection area while a cut-off portion is opened; calculating a secondcorrection spectrum by subtracting a second correction value calculatedbased on said second signal intensity from each component value of saidsecond spectrum; and calculating an output spectrum representing ameasurement result by subtracting each component value of said firstcorrection spectrum from a corresponding component value of said secondcorrection spectrum.